Multi-layer stack with embedded tamper-detect protection

ABSTRACT

Tamper-respondent assemblies and methods of fabrication are provided which include a multi-layer stack having multiple discrete component layers stacked and electrically connected together via a plurality of electrical contacts in between the component layers. Further, the tamper-respondent assembly includes a tamper-respondent electronic circuit structure embedded within the multi-layer stack. The tamper-respondent electronic circuit structure includes at least one tamper-respondent sensor embedded, at least in part, within at least one component layer of the multiple discrete component layers of the multi-layer stack. The tamper-respondent electronic circuit structure defines a secure volume within the multi-layer stack. For instance, the tamper-respondent electronic circuit structure may be fully embedded within the multi-layer stack, with monitor circuitry of the tamper-respondent electronic circuit structure residing within the secure volume within the multi-layer stack.

BACKGROUND

Many activities require secure electronic communications. To facilitatesecure electronic communications, an encryption/decryption system may beimplemented on an electronic assembly or printed circuit board assemblythat is included in equipment connected to a communications network.Such an electronic assembly is an enticing target for malefactors sinceit may contain codes or keys to decrypt intercepted messages, or toencode fraudulent messages. To prevent this, an electronic assembly maybe mounted in an enclosure, which is then wrapped in a security sensor,and encapsulated with polyurethane resin. A security sensor may be, inone or more embodiments, a web or sheet of insulating material withcircuit elements, such as closely-spaced, conductive lines fabricated onit. The circuit elements are disrupted if the sensor is torn, and thedisruption can be sensed in order to generate an alarm signal. The alarmsignal may be conveyed to a monitor circuit in order to reveal an attackon the integrity of the assembly. The alarm signal may also trigger anerasure of encryption/decryption keys stored within the electronicassembly.

In the above configuration, the electronic package, or tamper-proofelectronic package, may be difficult to test due to the presence of thesecurity sensor wrapped fully around the enclosure. Additionally, inthis configuration it is difficult to recover components from theelectronic package, for instance, should a manufacturing defect in thepackage be detected.

SUMMARY

Thus, provided herein, in one or more aspects, is a tamper-respondentassembly comprising a multi-layer stack including multiple discretecomponent layers stacked and electrically connected together via aplurality of electrical contacts in between the component layers; and atamper-respondent electronic circuit structure embedded within themulti-layer stack, the tamper-respondent electronic circuit structurecomprising at least one tamper-respondent sensor embedded, at least inpart, within at least one component layer of the multiple discretecomponent layers of the multi-layer stack, the tamper-respondentelectronic circuit structure defining a secure volume within themulti-layer stack. Further, the tamper-respondent electronic circuitstructure is embedded within the multi-layer stack, and the securevolume resides fully within the multi-layer stack.

In a further aspect, a method of fabricating a tamper-respondentassembly is provided which includes: providing a multi-layer stackcomprising multiple discrete component layers stacked and electricallyconnected together via a plurality of electrical contacts in between thecomponent layers; and embedding a tamper-respondent electronic circuitstructure within the multi-layer stack, the tamper-respondent electroniccircuit structure comprising at least one tamper-respondent sensorembedded, at least in part, within at least one component layer of themultiple discrete component layers of the multi-layer stack, thetamper-respondent electronic circuit structure defining a secure volumewithin the multi-layer stack. Further, the tamper-respondent electroniccircuit structure is embedded within the multi-layer stack, and thesecure volume resides fully within the multi-layer stack.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a partial cut-away of one embodiment of a tamper-proofelectronic package;

FIG. 2 is a cross-sectional elevational view of one embodiment of atamper-proof electronic package comprising an electronic circuit;

FIG. 3 depicts one embodiment of a tamper-respondent trace pattern orcircuit which may be employed within a tamper-respondent sensor, inaccordance with one or more aspects of the present invention;

FIG. 4A is a cross-sectional elevational view of another embodiment of atamper-proof electronic package, which includes a tamper-respondentsensor embedded within a multilayer circuit board, in accordance withone or more aspects of the present invention;

FIG. 4B is a top plan view of the multilayer circuit board of FIG. 4A,depicting one embodiment of the secure volume where defined, in part,within the multilayer circuit board, in accordance with one or moreaspects of the present invention;

FIG. 5A is a partial cross-sectional elevational view of a tamper-proofelectronic package comprising an electronic circuit with a multilayercircuit board and embedded tamper-respondent sensor, in accordance withone or more aspects of the present invention;

FIG. 5B is a schematic of a portion of the tamper-proof electronicpackage of FIG. 5A, in accordance with one or more aspects of thepresent invention;

FIG. 5C depicts an alternate embodiment of an electronic circuitcomprising a multilayer circuit board and an embedded tamper-respondentsensor, in accordance with one or more aspects of the present invention;

FIG. 6 illustrates one embodiment of a process for fabricating amultilayer circuit board with an embedded tamper-respondent sensor, inaccordance with one or more aspects of the present invention;

FIG. 7 is a plan view of one embodiment of a tamper-respondent mat layerfor a tamper-respondent sensor embedded within a multilayer circuitboard, in accordance with one or more aspects of the present invention;

FIG. 8A is a plan view of the tamper-respondent mat layer of FIG. 7,with conductive vias to an upper layer illustrated for electricallyconnecting to the conductive traces of the different circuit zones ofthe tamper-respondent mat layer, in accordance with one or more aspectsof the present invention;

FIG. 8B is a partial plan view of the tamper-respondent mat layer ofFIG. 8A, showing a portion of the conductive traces provided within twoadjacent circuit zones of the tamper-respondent mat layer, in accordancewith one or more aspects of the present invention;

FIG. 8C is a plan view of a wiring layer overlying the tamper-respondentmat layer of FIG. 8A, and illustrating an offsetting of the conductivevias from the tamper-respondent mat layer of FIG. 8A to selectedlocations within the wiring layer, which also accommodate (in thedepicted example) external signal line vias facilitating communicationto and from the secure volume associated with the multilayer circuitboard, in accordance with one or more aspects of the present invention;

FIG. 8D depicts a tamper-respondent mat layer above the wiring layer ofFIG. 8C, and illustrates further offsetting of conductive vias, from onemat layer to the next, to enhance security of the tamper-respondentsensor, in accordance with one or more aspects of the present invention;

FIG. 8E is a plan view of a first tamper-respondent frame above thetamper-respondent mat layer of FIG. 8D, which facilitates defining, inpart, the secure volume within the multilayer circuit board, inaccordance with one or more aspects of the present invention;

FIG. 8F is a partial depiction of conductive traces for atamper-respondent frame such as illustrated in FIG. 8E, in accordancewith one or more aspects of the present invention;

FIG. 8G is a plan view of a second tamper-respondent frame overlying thefirst tamper-respondent frame, and further facilitating defining thesecure volume in association with the multilayer circuit board, inaccordance with one or more aspects of the present invention;

FIG. 9 is a schematic illustration of one embodiment of monitorcircuitry and electrical interconnection of different circuit zones ofdifferent tamper-respondent layers of the tamper-respondent sensorwithin the secure volume associated with the multilayer circuit board,in accordance with one or more aspects of the present invention;

FIG. 10 is an elevational view of one embodiment of a tamper-respondentassembly comprising a multi-layer stack with an embeddedtamper-respondent electronic circuit structure, in accordance with oneor more aspects of the present invention;

FIG. 11A is a cross-sectional plan view of one embodiment of a sensorcomponent layer of the multi-layer stack of FIG. 10, taken along line11A-11A of FIG. 11B, and illustrating, in part, a mat-type,tamper-detect circuit within the sensor component layer, in accordancewith one or more aspects of the present invention;

FIG. 11B is a cross-sectional elevational view of the sensor componentlayer of FIG. 11A, taken along line 11B-11B thereof, and depictingmultiple mat-type, tamper-respondent circuits within the sensorcomponent, as well as multiple frame-type, tamper-detect circuits, inaccordance with one or more aspects of the present invention;

FIG. 12A depicts a sub-stack of multiple in-between component layers ofa multi-layer stack such as depicted in FIG. 10, and illustrates oneembodiment of at least one peripheral tamper-detect circuit facilitatingdefining a secure volume within the sub-stack, in accordance with one ormore aspects of the present invention;

FIG. 12B is a cross-sectional plan view of the structure of FIG. 12A,taken along line 12B-12B thereof, and showing one embodiment ofelectrical interconnect at the sensor component layer of the sub-stack,depicting an electrical stitch pattern for connecting through-substratevias within the in-between component layers of the sub-stack into the atleast one peripheral tamper-detect circuit, in accordance with one ormore aspects of the present invention; and

FIG. 13 depicts an alternate embodiment of a tamper-respondent assemblycomprising a multi-layer stack and an embedded tamper-respondentelectronic circuit structure, in accordance with one or more aspects ofthe present invention.

DETAILED DESCRIPTION

Aspects of the present invention and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting example(s) illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as not to unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific example(s), while indicating aspects of theinvention, are given by way of illustration only, and are not by way oflimitation. Various substitutions, modifications, additions, and/orarrangements, within the spirit and/or scope of the underlying inventiveconcepts will be apparent to those skilled in the art for thisdisclosure. Note further that reference is made below to the drawings,which are not drawn to scale for ease of understanding, wherein the samereference numbers used throughout different figures designate the sameor similar components. Also, note that numerous inventive aspects andfeatures are disclosed herein, and unless otherwise inconsistent, eachdisclosed aspect or feature is combinable with any other disclosedaspect or feature as desired for a particular application, forestablishing a secure volume for an electronic component or electroniccircuit to be protected.

Reference is first made to FIG. 1 of the drawings, which illustrates oneembodiment of an electronic assembly package 100 configured as atamper-proof electronic assembly package for purposes of discussion. Inthe depicted embodiment, an electronic assembly enclosure 110 isprovided containing, for instance, an electronic assembly, which in oneembodiment may include a plurality of electronic components, such as anencryption and/or decryption module and associated memory. Theencryption and/or decryption module may comprise security-sensitiveinformation with, for instance, access to the information stored in themodule requiring use of a variable key, and with the nature of the keybeing stored in the associated memory within the enclosure.

In one or more implementations, a tamper-proof electronic package suchas depicted is configured or arranged to detect attempts to tamper-withor penetrate into electronic assembly enclosure 110. Accordingly,electronic assembly enclosure 110 also includes, for instance, a monitorcircuit which, if tampering is detected, activates an erase circuit toerase information stored within the associated memory, as well as theencryption and/or decryption module within the communications card.These components may be mounted on, and interconnected by, a multi-layercircuit board, such as a printed circuit board or other multi-layersubstrate, and be internally or externally powered via a power supplyprovided within the electronic assembly enclosure.

In the embodiment illustrated, and as one example only, electronicassembly enclosure 110 may be surrounded by a tamper-respondent sensor120, an encapsulant 130, and an outer, thermally conductive enclosure140. In one or more implementations, tamper-respondent sensor 120 mayinclude a tamper-respondent laminate that is folded around electronicassembly enclosure 110, and encapsulant 130 may be provided in the formof a molding. Tamper-respondent sensor 120 may include various detectionlayers, which are monitored through, for instance, a ribbon cable by theenclosure monitor, against sudden violent attempts to penetrateenclosure 110 and damage the enclosure monitor or erase circuit, beforeinformation can be erased from the encryption module. Thetamper-respondent sensor may be, for example, any such articlecommercially available or described in various publications and issuedpatents, or any enhanced article such as disclosed herein.

By way of example, tamper-respondent sensor 120 may be formed as atamper-respondent laminate comprising a number of separate layers with,for instance, an outermost lamination-respondent layer including amatrix of, for example, diagonally-extending or sinusoidally-extending,conductive or semi-conductive lines printed onto a regular, thininsulating film. The matrix of lines forms a number of continuousconductors which would be broken if attempts are made to penetrate thefilm. The lines may be formed, for instance, by printing carbon-loadedPolymer Thick Film (PTF) ink onto the film and selectively connectingthe lines on each side, by conductive vias, near the edges of the film.Connections between the lines and an enclosure monitor of thecommunications card may be provided via, for instance, one or moreribbon cables. The ribbon cable itself may be formed of lines ofconductive ink printed onto an extension of the film, if desired.Connections between the matrix and the ribbon cable may be made viaconnectors formed on one edge of the film. As noted, the laminate may bewrapped around the electronic assembly enclosure to define thetamper-respondent sensor 120 surrounding enclosure 110.

In one or more implementations, the various elements of the laminate maybe adhered together and wrapped around enclosure 110, in a similarmanner to gift-wrapping a parcel, to define the tamper-respondent sensorshape 120. The assembly may be placed in a mold which is then filledwith, for instance, cold-pour polyurethane, and the polyurethane may becured and hardened to form an encapsulant 130. The encapsulant may, inone or more embodiments, completely surround the tamper-respondentsensor 120 and enclosure 110, and thus form a complete environmentalseal, protecting the interior of the enclosure. The hardenedpolyurethane is resilient and increases robustness of the electronicpackage in normal use. Outer, thermally conductive enclosure 140 mayoptionally be provided over encapsulant 130 to, for instance, providefurther structural rigidity to the electronic package.

FIG. 2 depicts in detail one embodiment of a tamper-proof electronicpackage 200. Electronic package 200 is defined by, for instance, a basemetal shell 202 and a top metal shell 204. Outer surfaces of base metalshell 202 and top metal shell 204 may be provided with standoffs 206,with an electronic assembly 208 resting on standoffs 206 defined in basemetal shell 202. Electronic assembly 208 may include, for instance, aprinted circuit board 210 with electronic components 212 that areelectrically connected via conductors (not shown) defined within or onprinted circuit board 210.

Hollow spacers 213 may be placed below dimples 206 in top metal shell204, and rivets 214 provided, extending through openings in dimples 206,through hollow spacers 213 and through openings in printed circuit board210 to base metal shell 202 in order to fixedly secure electronicassembly 208 within the enclosure formed by base and top metal shells202, 204. A security mesh or tamper-respondent sensor 216 is wrappedaround the top, base, and four sides of the enclosure formed by base andtop metal shells 202, 204. As illustrated, in one or more embodiments,top metal shell 204 may have an opening through which a bus 220 extends.One end of bus 220 may be connected to conductors (not shown) on printedcircuit board 210, and the other end may be connected to conductors (notshown) on a printed circuit board 222. As bus 220 passes through theopening, the bus extends between an inner edge region 223 of thesecurity mesh 216 and an overlapping, outer edge region 224 of thesecurity mesh 216. A group of wires 226 connect, in one embodiment,security mesh 216 to conductors on printed circuit board 210. Circuitryon printed circuit board 210 is responsive to a break or discontinuityin security sensor array 216, in which case, an alarm signal may beemitted on bus 220, and also encryption/decryption keys stored withinelectronic assembly 208 may be erased.

In one or more implementations, liquid polyurethane resin may be appliedto security mesh 216 and cured. An outer, thermally conductive enclosure228, such as a copper enclosure, may be filled with liquid polyurethaneresin with the electronic assembly and inner enclosure and security meshsuspended within it. Upon curing the resin, the electronic assembly andinner enclosure and security mesh become embedded in a polyurethaneblock or encapsulant 230, as shown. The enclosure 228 is mounted on theprinted circuit board 222, which can be accomplished using, forinstance, legs 240 which extend through slots in printed circuit board222 and terminate in flanges 242, which are then bent out of alignmentwith the slots. Bus 220 may be connected, by way of printed circuitboard 222 to connectors 244 located along, for instance, one edge ofprinted circuit board 222.

When considering tamper-proof packaging, the electronic package needs tomaintain defined tamper-proof requirements, such as those set forth inthe National Institutes of Standards and Technology (NIST) PublicationFIPS 140-2, which is a U.S. Government Computer Security Standard, usedto accredit cryptographic modules. The NIST FIPS 140-2 defines fourlevels of security, named Level 1 to Level 4, with Security Level 1providing the lowest level of security, and Security Level 4 providingthe highest level of security. At Security Level 4, physical securitymechanisms are provided to establish a complete envelope of protectionaround the cryptographic module, with the intent of detecting andresponding to any unauthorized attempt at physical access. Penetrationof the cryptographic module enclosure from any direction has a very highprobability of being detected, resulting in the immediate zeroization ofall plain text critical security parameters (CSPs). Security Level 4cryptographic modules are useful for operation in physically unprotectedenvironments. Security Level 4 also protects a cryptographic moduleagainst a security compromise due to environmental conditions orfluctuations outside of the module's normal operating ranges forvoltages and temperature. Intentional excursions beyond the normaloperating ranges may be used by an attacker to thwart the cryptographicmodule's defenses. The cryptographic module is required to eitherinclude specialized environmental protection features designed to detectfluctuations and zeroize critical security parameters, or to undergorigorous environmental failure testing to provide reasonable assurancethat the module will not be affected by fluctuations outside of thenormal operating range in a manner that can compromise the security ofthe module.

To address the demands of ever-improving anti-intrusion technology, andthe higher-performance encryption/decryption functions being provided,enhancements to the tamper-proof, tamper-evident packaging for theelectronic components or circuits at issue are desired. Variousenhancements are described hereinbelow to, for instance,tamper-respondent assemblies and tamper-respondent sensors. Note thatthe numerous inventive aspects described herein may be used singly, orin any desired combination. Additionally, in one or moreimplementations, the enhancements to tamper-proof electronic packagingdescribed herein may be provided to work within defined spacelimitations for existing packages. For instance, one or more of theconcepts described may be configured to work with peripheral componentinterconnect express (PCIe) size limits, and the limitations resultingfrom being capsulated in, for instance, an insulating encapsulant.

Thus, disclosed hereinbelow with reference to FIGS. 3-13 are variousapproaches and/or enhancements to creating a secure volume foraccommodating one or more electronic components, such as one or moreencryption and/or decryption modules or circuits and associatedcomponents of a communications card or other electronic assembly.

FIG. 3 depicts a portion of one embodiment of a tamper-respondent layer305 (or laser and pierce-respondent layer) of a tamper-respondent sensor300 or security sensor, such as discussed herein. In FIG. 3, thetamper-respondent layer 305 includes circuit lines or traces 301provided on one or both opposite sides of a flexible layer 302, which inone or more embodiments, may be a flexible insulating layer or film.FIG. 3 illustrates circuit lines 301 on, for instance, one side offlexible layer 302, with the traces on the opposite side of the filmbeing, for instance, the same pattern, but (in one or more embodiments)offset to lie directly below spaces 303, between circuit lines 301. Asdescribed below, the circuit lines on one side of the flexible layer maybe of a line width W₁ and have a pitch or line-to-line spacing W_(s)such that piercing of the layer 305 at any point results in damage to atleast one of the circuit lines traces 301. In one or moreimplementations, the circuit lines may be electrically connectedin-series or parallel to define one or more conductors which may beelectrically connected in a network to an enclosure monitor, whichmonitors the resistance of the lines, as described herein. Detection ofan increase, or other change, in resistance, caused by cutting ordamaging one of the traces, will cause information within the encryptionand/or decryption module to be erased. Providing conductive lines 301 ina pattern, such as a sinusoidal pattern, may advantageously make it moredifficult to breach tamper-respondent layer 305 without detection. Note,in this regard, that conductive lines 301 could be provided in anydesired pattern. For instance, in an alternate implementation,conductive lines 301 could be provided as parallel, straight conductivelines, if desired, and the pattern or orientation of the pattern mayvary between sides of a layer, and/or between layers.

As noted, as intrusion technology continues to evolve, anti-intrusiontechnology needs to continue to improve to stay ahead. In one or moreimplementations, the above-summarized tamper-respondent sensor 300 ofFIG. 3 may be disposed over an outer surface of an electronic enclosure,such as an electronic enclosure described above in connection with FIGS.1 & 2. Alternatively, as described further herein, the tamper-respondentsensor may cover or line an inner surface of an electronic enclosure toprovide a secure volume about at least one electronic component to beprotected. Still further, the tamper-respondent sensor, or moreparticularly, the tamper-detect circuit(s) of the sensor, could beembedded within a multi-layer stack, such as a multi-die stack, asdescribed below. Numerous enhancements to the tamper-respondent sensoritself are described below.

In one or more aspects, disclosed herein is a tamper-respondent sensor300 with circuit lines 301 having reduced line widths W₁ of, forinstance, 200 μm, or less, such as less than or equal to 100 μm, or evenmore particularly, in the range of 30-70 μm. This is contrasted withconventional trace widths, which are typically on the order of 350 μm orlarger. Commensurate with reducing the circuit line width W₁,line-to-line spacing width W_(s) 303 is also reduced to less than orequal to 200 μm, such as less than or equal to 100 μm, or for instance,in a range of 30-70 μm. Advantageously, by reducing the line width W₁and line-to-line spacing W_(s) of circuit lines 301 withintamper-respondent sensor 300, the circuit line width and pitch is on thesame order of magnitude as the smallest intrusion instruments currentlyavailable, and therefore, any intrusion attempt will necessarily removea sufficient amount of a circuit line(s) to cause resistance to change,and thereby the tamper intrusion to be detected. Note that, by makingthe circuit line width of the smaller dimensions disclosed herein, anycutting or damage to the smaller-dimensioned circuit line will also bemore likely to be detected, that is, due to a greater change inresistance. For instance, if an intrusion attempt cuts a 100 μm widthline, it is more likely to reduce the line width sufficiently to detectthe intrusion by a change in resistance. A change in a narrower linewidth is more likely to result in a detectable change in resistance,compared with, for instance, a 50% reduction in a more conventional linewidth of 350 μm to, for instance, 175 μm. The smaller the conductivecircuit line width becomes, the more likely that a tampering of thatline will be detected.

Note also that a variety of materials may advantageously be employed toform the circuit lines. For instance, the circuit lines may be formed ofa conductive ink (such as a carbon-loaded conductive ink) printed ontoone or both opposite sides of one or more of the flexible layers 302 ina stack of such layers. Alternatively, a metal or metal alloy could beused to form the circuit lines, such as copper, silver, intrinsicallyconductive polymers, carbon ink, or nickel-phosphorus (NiP), orOmega-Ply®, offered by Omega Technologies, Inc. of Culver City, Calif.(USA), or Ticer™ offered by Ticer Technologies, Chandler, Ariz. (USA).Note that the process employed to form the fine circuit lines or traceson the order described herein is dependent, in part, on the choice ofmaterial used for the circuit lines. For instance, if copper circuitlines are being fabricated, then additive processing, such as plating upcopper traces, or subtractive processing, such as etching away unwantedcopper between trace lines, may be employed. By way of further example,if conductive ink is employed as the circuit line material, fine circuitlines on the order disclosed herein can be achieved by focusing on therheological properties of the conductive ink formulation. Further,rather than simple pneumatics of pushing conductive ink through anaperture in a stencil with a squeegee, the screen emulsion may becharacterized as very thin (for instance, 150 to 200 μm), and a squeegeeangle may be used such that the ink is sheared to achieve conductive inkbreakaway rather than pumping the conductive ink through the screenapertures. Note that the screen for fine line width printing such asdescribed herein may have the following characteristics in one specificembodiment: a fine polyester thread for both warp and weave on the orderof 75 micrometers; a thread count between 250-320 threads per inch; amesh thickness of, for instance, 150 micrometers; an open area betweenthreads that is at least 1.5× to 2.0× the conductive ink particle size;and to maintain dimensional stability of the print, the screen snap-offis kept to a minimum due the screen strain during squeegee passage.

In one or more implementations, circuit lines 301 of tamper-respondentsensor 300 are electrically connected to define one or more resistivenetworks. Further, the circuit lines may include one or more resistivecircuit lines by selecting the line material, line width W₁ and linelength L₁, to provide a desired resistance per line. As one example, a“resistive circuit line” as used herein may comprise a line with 1000ohms resistance or greater, end-to-end. In one specific example, acircuit line width of 50 μm, with a circuit line thickness of 10 μm maybe used, with the line length L₁ and material selected to achieve thedesired resistance. At the dimensions described, good electricalconductors such as copper or silver may also be employed and still forma resistive network due to the fine dimensions noted. Alternatively,materials such as conductive ink or the above-noted Omega-Ply® or Ticer™may be used to define resistive circuit lines.

In a further aspect, the flexible layer 302 itself may be furtherreduced in thickness from a typical polyester layer by selecting acrystalline polymer to form the flexible layer or substrate. By way ofexample, the crystalline polymer could comprise polyvinylidenedifluoride (PVDF), or Kapton, or other crystalline polymer material.Advantageously, use of a crystalline polymer as the substrate film mayreduce thickness of the flexible layer 302 to, for instance, 2 milsthick from a more conventional amorphous polyester layer of, forinstance, 5-6 mils. A crystalline polymer can be made much thinner,while still maintaining structural integrity of the flexible substrate,which advantageously allows for far more folding, and greaterreliability of the sensor after folding. Note that the radius of anyfold or curvature of the sensor is necessarily constrained by thethickness of the layers comprising the sensor. Thus, by reducing theflexible layer thickness to, for instance, 2 mils, then in a fourtamper-respondent layer stack, the stack thickness can be reduced from,for instance, 20 mils in the case of a typical polyester film, to 10mils or less with the use of crystalline polymer films.

One or more aspects of the above-discussed tamper-respondent sensor ofFIG. 3 may be employed in the various tamper-respondent assembliesdescribed herein. By way of example, FIGS. 4A-9 depict an alternateapproach to creating a secure volume which utilizes one or moretamper-respondent sensors on an inner surface of an enclosure. Further,FIGS. 10-13 depict various embodiments of a multi-layer stack with anembedded tamper-respondent electronic circuit structure comprising oneor more tamper-respondent sensors embedded within the discrete componentlayers of the stack. The tamper-detect circuits of the one or moretamper-respondent sensors of the tamper-respondent assemblies of FIGS.10-13 may have one or more similar attributes to those described abovein connection with FIG. 3, or described below with reference to FIGS.4A-9.

As noted, FIGS. 4A & 4B depict one embodiment of an electronic package,or tamper-proof electronic package 400, comprising an electronic circuit415, in accordance with one or more aspects of the present invention.

Referring collectively to FIGS. 4A & 4B, electronic circuit 415 includesa multilayer circuit board 410 which has a tamper-respondent sensor 411embedded therein that facilitates defining, in part, a secure volume 401associated with multilayer circuit board 410 that extends intomultilayer circuit board 410. In particular, in the embodiment of FIGS.4A & 4B, secure volume 401 exists partially within multilayer circuitboard 410, and partially above multilayer circuit board 410. One or moreelectronic components 402 are mounted to multilayer circuit board 410within secure volume 401 and may comprise, for instance, one or moreencryption modules and/or decryption modules, and associated components,with the tamper-proof electronic package comprising, in one or moreembodiments, a communications card of a computer system.

Tamper-proof electronic package 400 further includes an enclosure 420,such as a pedestal-type enclosure, mounted to multilayer circuit board410 within, for instance, a continuous groove (or trench) 412 formedwithin an upper surface of multilayer circuit board 410. In one or moreembodiments, enclosure 420 may comprise a thermally conductive materialand operate as a heat sink for facilitating cooling of the one or moreelectronic components 402 within the secure volume. A security mesh 421,such as the above-described security meshes, may be associated withenclosure 420, for example, wrapping around the inner surface ofenclosure 420 to facilitate defining, in combination withtamper-respondent sensor 411 embedded within multilayer circuit board410, secure volume 401. In one or more implementations, security mesh421 extends down into continuous groove 412 in multilayer circuit board410 and may, for instance, even wrap partially or fully around the loweredge of enclosure 420 within continuous groove 412 to provide enhancedtamper detection where enclosure 420 couples to multilayer circuit board410. In one or more implementations, enclosure 420 may be securelyaffixed to multilayer circuit board 410 using, for instance, a bondingmaterial such as an epoxy or other adhesive.

As depicted in FIG. 4B, one or more external circuit connection vias 413may be provided within multilayer circuit board 410 for electricallyconnecting to the one or more electronic components 402 (FIG. 4A) withinsecure volume 401. These one or more external circuit connection vias413 may electrically connect to one or more external signal lines orplanes (not shown) embedded within multilayer circuit board 410 andextending, for instance, into a secure base region of (or below) securevolume 401, as explained further below. Electrical connections to andfrom secure volume 401 may be provided by coupling to such externalsignal lines or planes within the multilayer circuit board 410.

As noted with reference to FIGS. 4A & 4B, secure volume 401 defined inassociation with multilayer circuit board 410 may be sized to houseelectronic components 402 to be protected, and be constructed to extendinto multilayer circuit board 410. In one or more implementations,multilayer circuit board 410 includes electrical interconnect within thesecure volume 401 defined in the board, for instance, for electricallyconnecting the multiple tamper-respondent layers of the embeddedtamper-respondent sensor 411 to associated monitor circuitry alsodisposed within secure volume 401.

Note that the embodiment depicted in FIGS. 4A & 4B is presented by wayof example only. In one or more other implementations, the electroniccircuit may comprise multiple multilayer circuit boards, each with atamper-respondent sensor embedded within the multilayer circuit boardwith an appropriate connector, located within a secure volume definedbetween two adjacent multilayer circuit boards, interconnecting selectedwiring of the multilayer circuit boards. In such an implementation, theoverlying multilayer circuit board could be hollowed out to accommodate,for instance, the connector and/or one or more other electroniccomponents between the multilayer circuit boards. In addition, otherconfigurations of enclosure 420, and/or other approaches to couplingenclosure 420 and multilayer circuit board 410 may be employed.

By way of further example, FIG. 5A depicts a partial cross-sectionalelevational view of one embodiment of multilayer circuit board 410 andenclosure 420. In this configuration, the embedded tamper-respondentsensor includes multiple tamper-respondent layers including, by way ofexample, at least one tamper-respondent mat (or base) layer 500, and atleast one tamper-respondent frame 501. In the example depicted, twotamper-respondent mat layers 500 and two tamper-respondent frame 501 areillustrated, by way of example only. The lower-most tamper-respondentmat layer 500 may be a continuous sense or detect layer extendingcompletely below the secure volume being defined within multilayercircuit board 410. One or both tamper-respondent mat layers 500 belowsecure volume 401 may be partitioned into multiple circuit zones, asdiscussed further below. Within each tamper-respondent mat layer, ormore particularly, within each circuit zone of each tamper-respondentmat layer, multiple circuits or conductive traces are provided in anydesired configuration, such as the configuration described above inconnection with FIG. 3. Further, the conductive traces within thetamper-respondent layers may be implemented as, for instance, aresistive layer which is difficult to attach shunt circuits to, asexplained further below.

As illustrated, one or more external signal lines or planes 505 entersecure volume 401 between, in this embodiment, two tamper-respondent matlayers 500, and then electrically connect upwards into the secure volume401 through one or more conductive vias, arranged in any desiredlocation and pattern. In the configuration depicted, the one or moretamper-respondent frames 501 are disposed at least inside of the areadefined by continuous groove 412 accommodating the base of enclosure420. Together with security mesh 421 associated with enclosure 420,tamper-respondent frames 501 define secure volume 401 where extending,in part, into multilayer circuit board 410. With secure volume 401defined, at least in part, within multilayer circuit board 410, theexternal signal line(s) 505 may be securely electrically connected to,for instance, the one or more electronic components 402 (FIG. 4A)mounted to multilayer circuit board 410 within secure volume 401. Inaddition, the secure volume 401 may accommodate electricalinterconnection of the conductive traces of the multipletamper-respondent layers, for instance, via appropriate monitorcircuitry.

As illustrated by the schematic of FIG. 5B, added security may beprovided by extending tamper-respondent mat layers 500 (and if desired,tamper-respondent frames 501) outward past continuous groove 412accommodating enclosure 420. In this manner, a line of attack 510 may bemade more difficult at the interface between enclosure 420 andmultilayer circuit board 410 since the attack 510 would need to cleartamper-respondent mat layers 500, the bottom edge of security mesh 421associated with enclosure 420, as well as the tamper-respondent frames501 of the embedded tamper-respondent sensor.

FIG. 5C depicts a variation on the multilayer circuit board 410 of FIG.5A. In this embodiment, the embedded tamper-respondent sensor againincludes multiple tamper-respondent mat layers 500 and multipletamper-respondent frames 501, such as described above. Additionally, atri-plate structure is provided comprising one or more external signallines or layers 505 sandwiched between an upper ground plane 506 and alower ground plane 507. In this configuration, high-speed transfer ofsignals to and from the secure volume, and in particular, to and fromthe one or more electronic components resident within the secure volume,are facilitated.

Note also that, in this implementation, once within the secure volume isdefined within multilayer circuit board 410, conductive vias within thesecure volume between layers of multilayer circuit board 410 may beeither aligned, or offset, as desired, dependent upon theimplementation. Alignment of conductive vias may facilitate, forinstance, providing a shortest connection path, while offsettingconductive vias between layers may further enhance security of thetamper-proof electronic package by making an attack into the securevolume through or around one or more tamper-respondent layers of themultiple tamper-respondent layers more difficult.

Each tamper-respondent layer of the embedded tamper-respondent sensorformed within the multilayer circuit board of the electronic circuit orelectronic package may include multiple conductive traces or linesformed between, for instance, respective sets of input and outputcontacts or vias at the trace termination points. Any number ofconductive traces or circuits may be employed in defining atamper-respondent layer or a tamper-respondent circuit zone within atamper-respondent layer. For instance, 4, 6, 8, etc., conductive tracesmay be formed in parallel (or otherwise) within a giventamper-respondent layer or circuit zone between the respective sets ofinput and output contacts to those conductive traces.

In one or more implementations, the multilayer circuit board may be amultilayer wiring board or printed circuit board formed, for instance,by building up the multiple layers of the board. FIG. 6 illustrates oneembodiment for forming and patterning a tamper-respondent layer withinsuch a multilayer circuit board.

As illustrated in FIG. 6, in one or more implementations, atamper-respondent layer, such as a tamper-respondent mat layer or atamper-respondent frame disclosed herein, may be formed by providing amaterial stack comprising, at least in part, a structural layer 601,such as a pre-preg (or pre-impregnated) material layer, a trace materiallayer 602 for use in defining the desired trace patterns, and anoverlying conductive material layer 603, to be patterned to defineconductive contacts or vias electrically connecting to the pattern oftraces being formed within the trace material layer 602, for instance,at trace terminal points. In one or more implementations, the tracematerial layer 602 may comprise nickel phosphorous (NiP), and theoverlying conductive layer 603 may comprise copper. Note that thesematerials are identified by way of example only, and that other traceand/or conductive materials may be used within the build-up layer orstack 600.

A first photoresist 604 is provided over stack 600, and patterned withone or more openings 605, through which the overlying conductive layer603 may be etched. Depending on the materials employed, and the etchprocesses used, a second etch process may be desired to remove portionsof trace material layer 602 to define the conductive traces of thesubject tamper-respondent layer. First photoresist 604 may then beremoved, and a second photoresist 604′ is provided over the conductivelayer 603 features to remain, such as the input and output contacts.Exposed portions of conductive layer 603 are then etched, and the secondphotoresist 604′ may be removed, with any opening in the layer beingfilled, for instance, with an adhesive (or pre-preg) and a next build-uplayer is provided, as shown. Note that in this implementation, most ofoverlying conductive layer 603 is etched away, with only the conductivecontacts or vias remaining where desired, for instance, at the terminalpoints of the traces formed within the layer by the patterning of thetrace material layer 602. Note that any of a variety of materials may beemployed to form the conductive lines or traces within atamper-respondent layer. Nickel-phosphorous (NiP) is particularlyadvantageous as a material since it is resistant to contact by solder,or use of a conductive adhesive to bond to it, making it harder tobridge from one circuit or trace to the next during an attempt topenetrate into the protected secure volume of the electronic circuit.Other materials which could be employed include OhmegaPly®, offered byOhmega Technologies, Inc., of Culver City, Calif. (USA), or Ticer™,offered by Ticer Technologies of Chandler, Ariz. (USA).

By way of example, FIG. 7 is a partial plan view of one embodiment of atamper-respondent mat layer 500 of an embedded tamper-respondent sensorwithin a multilayer circuit board, in accordance with one or moreaspects of the present invention. In this implementation,tamper-respondent mat layer 500 is divided into multipletamper-respondent circuit zones 701, 702, 703, 704, 705, of varyingsizes. Within each tamper-respondent circuit zone 701, 702, 703, 704,705, conductive traces of the same or different wiring patterns may beprovided with, for instance, the larger circuit zones 701, 703, 705,having a same number of traces and similar resistance per trace, perzone. Note that other configurations of tamper-respondent sense zonesmay be employed, including, for instance, equal or standard-sizedcircuit zones within a common tamper-respondent layer.

FIGS. 8A-8G depict, by way of example, one embodiment of multipletamper-respondent layers, and the electrical interconnect associatedwith the tamper-respondent layers, such as for, for instance, theembedded tamper-respondent sensor depicted in FIG. 5A.

As illustrated in FIG. 8A, blind contact vias 710, 711 are provided, byway of example, at the edge or boundary of each tamper-respondentcircuit zone 701, 702, 703, 704, 705 within a lowermosttamper-respondent mat layer 500. Contact vias 710, 711 facilitateelectrical connection from the ends of the conductive traces (not shown)of the depicted tamper-respondent layer upwards into the secure volumefor connection to appropriate monitor circuitry in any desiredconfiguration. Note with respect to FIG. 8A, that there are nopenetrations through the lowermost tamper-respondent mat layer 500. Asexplained further below, in one or more implementations, electricalinterconnect may be provided above the lowermost tamper-respondent matlayer to shift the overlying contact vias to, for instance, the centersof tamper-respondent circuit zones 702, 704, for instance, to preventdirect penetration of one tamper-respondent layer from passing throughother tamper-respondent layers. As noted, any desired number and size ofcircuit zones of traces may be defined within a tamper-respondent layer.In one or more implementations, a tamper-respondent mat layer mayinclude, for instance, 20, 30, 40, or more, tamper-respondent circuitzones within the layer, each with a same number of traces.

FIG. 8B is a partial enlarged depiction of tamper-respondent mat layer500 of FIG. 8A, showing a partial boundary between two tamper-respondentcircuit zones 701, 702, with input contacts or vias 710 depicted. Inthis example, an 8-band trace pattern of conductive traces or lines 800is partially shown within circuit zones 701, 702. As noted, the patternof conductive traces 800 may be provided in any desired configurationand include, for instance, saw-tooth or sinusoidal line portions withinthe respective circuit zones 701, 702. FIG. 8B depicts an example of thestart of a pattern of the conductive traces 800 where connected to inputcontacts or vias 710. Configuring conductive traces 800 as illustratedfurther enhances security by making it harder to reach multiple vias tojump over or shut sections of circuitry within a particulartamper-respondent layer of the embedded tamper-respondent sensor. In oneor more implementations the trace fill pattern is dense. Further,line-to-line or trace-to-trace spacing between the different circuitzones of a particular tamper-respondent layer may be the same as thatemployed within a particular tamper-respondent circuit zone.

FIG. 8C depicts an electrical interconnect layer over tamper-respondentmat layer 500 of FIG. 8A, with wiring illustrated to shift theconductive contacts to offset the vias to, by way of example, the middleof tamper-respondent circuit zones 702, 704. Additionally, thisinterconnect layer may comprise the external signal lines and contactsfor connecting to and from the secure volume to external the securevolume, including, if desired, the provision of one or more high-speedinterconnect circuits sandwiched between, for instance, respectiveground planes, such as noted above with reference to the exemplaryembodiment of FIG. 5C. As illustrated, conductive lines 811 may beprovided in this layer electrically connecting contacts 710, 711 of therespective tamper-respondent circuit zones to offset vias 812, 813disposed, for instance, in alignment 810 over tamper-respondent circuitzones 702, 704. In addition, one or more external signal line contacts815 may also be provided in this electrical interconnect layer forfacilitating electrical connection of the external signal lines into thesecure volume.

FIG. 8D depicts a second tamper-respondent mat layer 500, which in thisexample, is disposed above tamper-respondent mat layer 500 discussedabove in connection with FIGS. 8A & 8B. This second tamper-respondentmat layer 500 is similar to the first except, in the depictedembodiment, the sizes of the tamper-respondent circuit zones 721, 722,723, 724, 725, are different from the tamper-respondent circuit zones701, 702, 703, 704, 705, of the tamper-respondent mat layer 500 of FIGS.8A & 8B. Thus, the boundaries between the tamper-respondent circuitzones between the different layers are offset. This advantageouslyreduces the opportunity to penetrate both tamper-respondent mat layersalong a zone boundary or seam. Depending upon the implementation,electrical contacts to the depicted circuit vias or contacts in thetamper-respondent circuit zones depicted may extend directly upwardsinto the secure volume. Alternatively, contact vias may be furtheroffset into, for instance, the center lines of tamper-respondent circuitzones 722, 724, in a manner similar to that described above inconnection with FIG. 8C. As described above, within eachtamper-respondent circuit zone 721-725, a pattern of conductive traces(not shown) is provided. In one or more implementations,tamper-respondent mat layer 500 depicted in FIG. 8D may again compriseany desired number of circuit zones, such as 20, 30, 40, or more,circuit zones, each of which electrically connects within the securevolume in any desired monitor circuitry configuration. Note also that,in one or more embodiments, contacts or vias from the signal layer(s)and/or the lowermost tamper-respondent may layer, may extend throughthis second tamper-respondent mat layer.

FIG. 8E depicts an exemplary embodiment of a tamper-respondent frame 501of a tamper-respondent sensor, in accordance with one or more aspects ofthe present invention. Tamper-respondent frame 501 resides over thetamper-respondent mat layers 500 described above in connection withFIGS. 8A-8D, and is in one or more embodiments, a picture frame-typelayer which completely encircles, and thus serves to define, the securevolume 401 (FIGS. 4A & 5A) within the multilayer circuit board. Thetamper-respondent frame illustrated may be a first tamper-respondentframe 501, which provides protective sense wiring or traces, either onthe inside or the outside of the enclosure 420 (see FIGS. 4A & 5A),where coupled to the continuous groove or trench within the multilayercircuit board.

FIG. 8F depicts an exemplary embodiment of conductive contacts or vias710, 711 for tamper-respondent frame 501 of FIG. 8E, with four tracelines being depicted, by way of example only. As illustrated, the inputcontacts 710 and output contacts 711 at the trace terminal points in aparticular zone may be disposed in close proximity with the trace lines801 of tamper-respondent frame 501, and overlap or double back at theseam to minimize possibility of a successful attack throughtamper-respondent frame 501 at the seam.

FIG. 8G depicts a second tamper-respondent frame 501, which in one ormore embodiments, overlies the first tamper-respondent frame 501 of FIG.8E (in the example of FIG. 5A), and which may be identical to the firsttamper-respondent frame, except rotated 180° so that the wiring contacts710, 711 are separated from the layer below, as illustrated. As with thetamper-respondent mat layers 500, tamper-respondent frames 501 may bedivided into distinct circuit zones to, for instance, further enhancesecurity. For instance, 2, 4, 6, or more, circuit zones may be definedwithin a particular tamper-respondent frame 501, each with a pluralityof conductive traces defined between input contacts 710 and outputcontacts 711 at the trace terminal points.

The trace lines or circuits within all of the tamper-respondent layers,and in particular, the tamper-respondent circuit zones, of the embeddedtamper-respondent sensor are electrically connected into monitor orcompare circuitry 900 provided, for instance, within secure volume 401of multilayer circuit board 410, as illustrated in FIG. 9. Monitorcircuitry 900 may include various bridge or compare circuits, andconventional printed wiring board electrical interconnect inside thesecure volume 401, for instance, located within the secure volumedefined by the tamper-respondent frames 501 (FIG. 5A), and thetamper-respondent mat layers.

Note that advantageously, different tamper-respondent circuit zones ondifferent tamper-respondent layers may be electrically interconnectedinto, for instance, the same comparator circuit or Wheatstone bridge ofthe monitor circuitry. Thus, any of a large number of interconnectconfigurations may be possible. For instance, if each tamper-respondentmat layer contains 30 tamper-respondent circuit zones, and eachtamper-respondent frame contains four tamper-respondent circuit zones,then, for instance, the resultant sixty-eight tamper-respondent circuitzones may be connected in any configuration within the secure volume tocreate the desired arrangement of circuit networks within the securevolume being monitored for changes in resistance or tampering. Note inthis regard, that the power supply or battery for the tamper-respondentsensor may be located external to the secure volume, with the sensorbeing configured to trip and destroy any protected or critical data ifthe power supply or battery is tampered with.

By way of further enhancement, FIGS. 10-13 depict various furtherembodiments of a tamper-respondent assembly or tamper-proof electronicpackage, in accordance with one or more aspects of the presentinvention. In these configurations, rather than overlying or surroundingthe electronic component(s) or assembly to be protected, the sensorarray or circuitry of the tamper-respondent electronic circuit structureis embedded directly within a 2.5D or 3-D multi-layer stack comprisingone or more electronic components or circuits to be protected. Note thatas used herein, a “component layer” of the multi-layer stack refers to,for instance, a die, an integrated circuit chip, a wafer, an integratedcircuit layer, etc., comprising one or more electronic circuits. By wayof specific example, one or more electronic circuits to be protectedwithin the secure volume may comprise an encryption module and/ordecryption module with associated circuits, such as memory, cache, etc.

In general, a tamper-respondent assembly in this embodiment includes amulti-layer stack comprising multiple discrete component layers stackedand electrically connected together via a plurality of electricalcontacts in between the component layers; and a tamper-respondentelectronic circuit structure embedded within the multi-layer stack. Thetamper-respondent electronic circuit structure includes at least onetamper-respondent sensor embedded, at least in part, within at least onecomponent layer of the multiple discrete component layers of themulti-layer stack. The tamper-respondent electronic circuit structuredefines a secure volume within the multi-layer stack. As noted, in oneor more implementations, there may be two or more component layers(e.g., two or more die, chips, wafers, or other substrates withelectronic circuitry, etc.) in the multi-layer stack.

In one or more implementations, the multi-layer stack includes a firstcomponent layer, at least one in-between component layer, and a secondcomponent layer, stacked together. The at least one in-between componentlayer is disposed in between the first component layer and the secondcomponent layer in the multi-layer stack, and the tamper-respondentelectronic circuit structure is associated with, for instance, embeddedat least in part within, the first component layer, the at least onein-between component layer, and the second component layer, with thesecure volume being, at least in part, defined within the at least onein-between component layer.

By way of example, the at least one tamper-respondent sensor may includeat least one lower tamper-detect circuit within the first componentlayer, and at least one upper tamper-detect circuit within the secondcomponent layer. Further, the at least one tamper-respondent sensor mayinclude at least one peripheral tamper-detect circuit defined, at leastin part, by a plurality of through-substrate vias extending through theat least one in-between component layer. The at least one uppertamper-detect circuit, the at least one lower tamper-detect circuit, andthe at least one peripheral tamper-detect circuit electrically connectto monitor circuitry of the tamper-respondent electronic circuitstructure, and facilitate defining the secure volume within themulti-layer stack. The monitor circuitry itself may be disposed withinthe secure volume defined within the multi-layer stack.

In one or more examples, the at least one peripheral tamper-detectcircuit may extend between the at least one upper tamper-detect circuitand the at least one lower tamper-detect circuit, and be disposed aboutthe periphery of the at least one in-between component layer. In one ormore embodiments, the multi-layer stack may further include or reside ona base component layer, with the base component layer being (forexample) a 2.5D interposer. In one or more other implementations, thebase component layer may be a more typical chip substrate layer, such asinterconnect fan-out substrate to which a chip or a chip stack ismounted. Still further, in one or more embodiments, the multi-layerstack could mount directly to a circuit board, without an interveningbase component layer.

In one or more implementations, the multi-layer stack may includemultiple in-between component layers disposed between the firstcomponent and the second component layer. Further, the at least onetamper-respondent sensor may include at least one peripheraltamper-detect circuit which includes, or is defined by, respectivepluralities of through-substrate vias, each plurality ofthrough-substrate vias extending through a respective component layer ofthe multiple in-between component layers. At least somethrough-substrate vias of the respective pluralities ofthrough-substrate vias are aligned, and are electrically interconnectedin the at least one peripheral tamper-detect circuit by respectiveelectrical contacts of the plurality of electrical contacts disposed inbetween component layers of the multi-layer stack. Further, aconventional under-fill material may be disposed between adjacentcomponent layers of the multiple discrete component layers. Theunder-fill material may surround, at least in part, electrical contactsof the plurality of electrical contacts in between the component layers,including electrical contacts forming part of the at least oneperipheral tamper-detect circuit.

In one or more implementations, the at least one tamper-respondentsensor embedded, at least partially, within the at least one componentlayer, may comprise multiple aligned or stacked tamper-detect circuitswithin the one component layer of the at least one component layer ofthe multi-layer stack. For instance, multiple mat-type, tamper-detectcircuits may be disposed in a first, lower component layer and/or asecond, upper component layer of the multi-layer stack. As a specificexample, one or more mat-type, tamper-detect circuits may be disposedadjacent to each main surface of the two opposing main surfaces of thecomponent layer, for instance, in a lower component layer or uppercomponent layer of the multi-layer stack facilitating defining thesecure volume therein. In one or more embodiments, the tamper-respondentelectronic circuit structure is fully embedded within the multi-layerstack, and the secure volume resides fully within the multi-layer stack.

An anti-tamper, anti-intrusion, tamper-respondent assembly such assummarized above, with a multi-layer stack and an embeddedtamper-respondent electronic circuit structure, may be implemented invarious configurations, several examples of which are described belowwith reference to FIGS. 10-13. In general, the tamper-respondentassembly may include one or more of: input/output electrical contacts orbumps to communicate with circuitry outside the multi-layer stack, forinstance, for facilitating encrypting/decrypting of secure informationwithin the multi-layer stack; power and ground contacts or bumps topower the function(s) of the tamper-respondent assembly; upper and/orlower sensor components; peripheral tamper-detect circuitry comprising,for instance, one or more layers of through-silicon vias, through-glassvias, through-encapsulant vias, or other similar structure (generallyreferred to herein as through-substrate vias), to function as anedge-tamper-detect circuit; monitor or compare circuitry to detect anyattempt at intrusion into the tamper-respondent assembly; an optionalencryption/decryption engine (or other electronic circuit to beprotected); and/or other processes as needed for the tamper-respondentassembly to function for an intended purpose. Further, note that thetamper-respondent assembly may include a variety of circuitconfigurations and functions within the secure volume. For instance, oneor more integrated fiber optic circuits may be provided within thetamper-respondent assembly for communicating with other components orentities external to the assembly for faster and more securecommunications.

FIG. 10 depicts one embodiment of a tamper-respondent assembly,generally denoted 1000, in accordance with one or more aspects of thepresent invention. In this embodiment, tamper-respondent assembly 1000includes a multi-layer stack 1010 which includes, or resides on, by wayof example, a base component layer 1011 comprising (for instance) a 2.5Dinterposer, or alternatively any typical chip substrate (such as asubstrate with electrical interconnect fan-out). Base component layer1011 may couple to (for instance) a multilayer circuit board 1001, suchas a printed circuit board or motherboard. Note that in alternateconfigurations, the multi-layer stack 1010 could couple directly tomultilayer circuit board 1001, without an intervening base componentlayer, such as a substrate interposer. In the depicted example, athermally conductive cap 1020 resides over multi-layer stack 1010 and issealed to or in contact with the base component layer 1011, again by wayof example only. Additionally, a thermal interface material 1021 may beprovided between, for instance, an upper surface of multi-layer stack1010 and cap 1020. A heat sink 1025, such as an air-cooled heat sink, ora liquid-cooled heat sink, may be coupled to cap 1020, or alternatively,may be coupled to multi-layer stack 1010 directly in the absence of cap1020.

A tamper-respondent electronic circuit structure 1030 is embedded withinmulti-layer stack 1010, and includes at least one tamper-respondentsensor (e.g., 1032, 1033, 1034) embedded, at least in part, within atleast one component layer 1012, 1013, 1015 of the multiple discretecomponent layers of multi-layer stack 1010, and includes monitorcircuitry 1031 for monitoring the at least one tamper-respondent sensorfor a tamper event. Monitor circuitry 1031 is configured and connectedto monitor for a tamper event similar to the monitor or comparecircuitry described above in connection with the tamper-proof electronicpackages of FIGS. 1-9. Advantageously, monitor circuitry 1031 may bedisposed within one or more of the component layers 1012, 1013, 1015 inthe multi-layer stack 1010, and in particular, within the secure volume1040 defined by the sensor array within the multi-layer stack 1010.

In one or more implementations, the at least one tamper-respondentsensor includes at least one lower tamper-detect circuit 1032, at leastone upper tamper-detect circuit 1033, and at least one peripheraltamper-detect circuit 1034. Advantageously, these tamper-detect circuitsare formed within the component layers themselves using, for instance,conventional integrated circuit processes, such as back-end-of-line(BEOL) processes and conventional through-substrate via formationprocesses. Together, the tamper-detect circuits are configured andelectrically connected to the monitor circuitry to define secure volume1040 in three dimensions, fully embedded within the multi-layer stack1010, and sized to accommodate any number of electronic devices,components, modules, circuits, etc., to be protected within the stack.As one example, the secure volume may be sized and configured toaccommodate an encryption and/or decryption processor, as well asencryption and/or decryption keys.

In one or more implementations, sensor component layers 1012, 1013 maycomprise similarly configured tamper-detect circuits. By way of example,FIGS. 11A & 11B depict a partial implementation of sensor componentlayer 1012. As noted, sensor component layer 1013 may be similarlyconfigured, at least in terms of the tamper-detect circuits employed (inone example), however, possibly inverted in orientation withinmulti-layer stack 1010 of FIG. 10. Alternatively, those skilled in theart will note that sensor component layer 1013 could be differentlyconfigured, provided that the desired at least one upper tamper-detectcircuit is provided within that sensor component layer in order tofacilitate defining the sensor array comprising the secure volume withinthe multi-layer stack.

Referring to FIG. 11A, sensor component layer 1012 may comprise asubstrate 1100 with, for instance, at least one lower tamper-detectcircuit 1032 formed in association with substrate 1100 and extendingoutward to a periphery 1101 substantially aligned to the edge of themain opposing surfaces of the component layer. Depending on theimplementation, substrate 1100 may have or be a substantiallycrystalline substrate material (e.g., bulk silicon), whereas in otherembodiments, substrate 1100 may be formed on the basis of asilicon-on-insulator (SOI) architecture, in which a buried insulatinglayer may be provided below a circuit or interconnect layer. Other typesof substrates 1100 may be used, including, for instance, n-type orp-type doped substrates, silicon-germanium substrates, or may include orbe a non-semiconductor material.

As illustrated in FIG. 11B, the at least one lower tamper-detect circuit1032 may include multiple mat-type, tamper-detect circuits 1110 (orcircuit layers) and one or more frame-type, tamper-detect circuits 1111(or circuit layers). By way of example, the tamper-detect circuits ofthe at least one lower tamper-detect circuit 1032 may be formed asfront-end-of-line (FEOL) layers/structures and/or back-end-of-line(BEOL) layers/structures, depending on the desired implementation. Forinstance, existing processes for forming integrated circuits may beemployed to form tamper-respondent sensors of the patterns describedherein and depicted, by way of example, in FIGS. 3 and/or 5A-8G. Thesetamper-respondent detect circuits may be embedded or formed, forinstance, above an active layer of substrate 1100 and/or at a backsurface of substrate 1100, and may be electrically connected, via one ormore electrical contacts in between component layers of the multi-layerstack to the monitor circuitry 1031 (FIG. 10) disposed, for instance,within the secure volume of the tamper-respondent assembly. By way ofexample, BEOL layers/structures may conventionally include a pluralityof interleaved BEOL dielectric layers and BEOL metallization layers.Thus, forming the at least one lower tamper-detect circuit 1032 on orwithin substrate 1100 may comprise employing conventional BEOL processesto form the desired tamper-detect circuit patterns stacked one over theother, for instance, in different metal levels using conventionalback-end-of-line (BEOL) processing techniques.

By way of further explanation, the tamper-detect circuits may compriseconductive lines, for instance, formed of a metal such as copper or acopper alloy, spaced apart by a dielectric material, and configured as acontinuous protective or sense layer across or parallel to either orboth of the opposite main surfaces of substrate 1100. In one or moreother implementations, separate zones may be formed within theindividual tamper-detect circuits of the at least one lowertamper-detect circuit 1032 in a manner analogous to that described abovein connection with FIGS. 8A-8G. As noted, the multi-layer stack 1010 ofFIG. 10 will include input/output lines extending, in one or moreembodiments, through sensor component layer 1012, to electricalcontacts, such as conductive bumps, between and electrically connectingsensor component layer 1012 to, for instance, 2.5D interposer 1011 (FIG.10), and thus to external circuitry.

Additionally, power and ground planes (not shown) for the multi-layerstack could be provided through sensor component layer 1012. These lineswould extend through or around or in between the mat-type, tamper-detectcircuit layers 1110 (FIG. 11B) of the at least one lower tamper-detectcircuit 1032 depicted in FIGS. 11A & 11B. Note that inclusion of one ormore frame-type tamper-detect circuits 1111 within or as part of the atleast one lower tamper-detect circuit 1032 facilitates extending thesecure volume of the multi-layer stack into sensor component layer 1012.Advantageously, by extending the secure volume into sensor componentlayer 1012, and by analogy, into sensor component layer 1013, then inthe embodiment of FIG. 10, additional circuitry may be protected in thesecure volume, including for instance, the below-discussed peripheralinterconnect lines or stitching for the at least one peripheraltamper-detect circuit 1034 (FIG. 10), which may be disposed on thesensor component layers 1012, 1013.

FIGS. 12A & 12B depict in greater detail a sub-stack 1200 of multi-layerstack 1010 of FIG. 10. In FIG. 12A, sub-stack 1200 is shown to includemultiple in-between component layers 1015, each of which may includeactive circuitry, such as encrypt/decrypt circuitry, memory circuitry,cache circuitry, etc., as well as monitor circuitry 1031 of thetamper-respondent electronic circuit structure embedded within themulti-layer stack. Note that the three in-between component layerexample of FIGS. 10 & 12A is presented by way of example only. Forinstance, discussed below with reference to FIG. 13 is an alternateexample, wherein there is a single in-between component layer.

Continuing with FIG. 12A, sub-stack 1200 is shown to include the atleast one peripheral tamper-detect circuit 1034 of the at least onetamper-respondent sensor embedded, in part, within one or more componentlayers 1015 of the multiple discrete component layers of the multi-layerstack. In particular, in this example, the at least one peripheraltamper-detect circuit 1034 includes respective pluralities ofthrough-substrate vias 1201 extending through and disposed around theperipheries of respective component layers 1015 of sub-stack 1200. Asdepicted, respective electrical contacts 1202 are disposed in betweenaligned through-substrate vias 1201 in adjacent component layers 1015 ofsub-stack 1200, and together with interconnect lines or stitching 1210on upper and lower sensor component layers 1012, 1013, one or moreperipheral tamper-detect circuits 1034 are formed extending, forexample, in a vertically-oriented, continuous sinusoidal manner aboutthe periphery of sub-stack 1200.

In one or more examples, the in-between component layers 1015 maycomprise respective substrates that include a semiconductor material,such as a crystalline material. For instance, the substrates may includesilicon. Other types of semiconductor materials, such assilicon-germanium (SiGe), germanium (Ge), gallium-arsenic (GaAs), or anyother suitable semiconductor materials, including subsequently developedmaterials, may also be used as or in association with the substrate. Theinitial thickness of the substrates may be, for instance, about 500-800μm, and the substrates may be processed to have a final thickness of,for example, about 50-100 μm. Note that the substrate thicknesses mayvary depending upon component layer and application, or the integratedcircuits formed within, for instance, the active region of therespective component layer. Further, note that the initial and finalthicknesses may vary depending on the methodology used and the depth ofthe through-substrate vias 1201 which are formed. By way of example,each through-substrate via (or through-substrate via conductor) mayinclude, for instance, a conductive material such as copper or a copperalloy. Other types of conductive materials, such as aluminum, tungsten,gold, silver, tin, other metals, or alloys thereof, may also be used toform the through-substrate vias 1201. The diameter of thethrough-substrate vias may range from, for instance, 10-25 μm, and thedepth of the through-substrate vias may range, for instance, from about20-100 μm. Other diameters and depths of through-substrate vias may alsobe useful. In one specific embodiment, the size of the through-substratevia is about 25 μm (diameter) by 50-60 μm (depth).

Further, note that the plurality of electrical contacts 1202electrically connecting aligned through-substrate vias 1201 of adjacentin-between component layers 1015 may comprise micro-sized electricalcontacts, such as, micro-C4 bumps, such as micro-C4 solder bumps. By wayof specific example, the micro-C4 bumps may be about 25-30 μm indiameter, by about 30 μm high. Note in this regard, that the pluralityof through-substrate vias 1201 in each respective component layer 1015are disposed to form closely spaced, vertical tamper-detect lines of theat least one peripheral tamper-detect circuit 1034. In one or moreimplementations, the through-substrate vias 1201 may be spaced, forinstance, 20-30 μm apart, such as about 25 μm apart. Those skilled inthe art will understand that the spacing distance depends, in part, onthe integrated circuit process technology employed to form thetamper-respondent sensor(s) of the tamper-respondent electronic circuitstructure in the three-dimensional configuration of FIGS. 10-13.

As illustrated in FIG. 12B, and the cross-sectional view of FIG. 10,multiple continuous rows of through-substrate vias 1201 may be formedwithin the in-between component layers 1015 of the multi-layer stack,with three rows from the edge of each component layer inward beingdepicted, by way of example only. A single row, or two rows, or anynumber of rows, could be formed, depending on the tamper-detectapplication. Note also, that in this example, the alignedthrough-substrate vias 1201 are electrically connected in-seriesvertically by aligned interconnecting electrical contacts 1202 inbetween the component layers.

As noted, FIG. 12B is by way of example a cross-sectional plan view ofone embodiment of the sub-stack 1200 of FIG. 12A at upper sensorcomponent layer 1013 of multi-layer stack 1010. As illustrated, in oneor more embodiments, the plurality of electrical contacts 1202 disposedover respective aligned columns of through-substrate vias 1201 (FIG.12A) extending through in-between component layers 1015 are electricallyconnected via respective electrical interconnect lines or stitching1210. These interconnect lines 1210 (or stitch connections) are shown toalternate, with a similar but offset pattern of interconnect lines beingprovided on lower sensor component 1012 (FIG. 12A) such that thevertically-oriented, sinusoidal configuration of FIG. 12A is obtainedfor the at least one peripheral tamper-detect circuit 1034 (FIG. 12A).Note that various conductive materials and line widths may be employedto interconnect the adjacent electrical contacts 1202 in the patternsdepicted in FIG. 12B. By way of example, copper conductors could beemployed at or near a surface of upper sensor component layer 1013 usingback-end-of-line (BEOL) processing. The conductive lines could be, inone or more implementations, 5-15 μm wide, such as 10 μm wide. Note thatthe pattern depicted in FIG. 12B is continuous and facilitates defining,in combination with the respective pluralities of through-substrate vias1201 (FIG. 12A) and in-between electrical contacts 1202, thevertically-extending, peripheral tamper-detect circuit(s) of thetamper-respondent sensor. Note also that the particular wiringconfiguration being monitored by monitor circuitry 1031 within thesecure volume may vary from implementation to implementation. In oneimplementation, the rows of peripheral tamper-detect circuitry may beconnected in a single tamper-detect circuit, while in otherconfigurations, separate tamper-detect circuits may be connected to themonitor circuitry within the secure volume, as desired. Further, notethat the rows of through-substrate vias could be connected in anydesired configuration of tamper-detect circuits, with thevertically-oriented, sinusoidal configuration depicted being provided asone example only. For instance, increased security may be provided byelectrically interconnecting the through-substrate vias in a more randomconfiguration.

By way of further example, FIG. 13 depicts an alternate embodiment of atamper-respondent assembly 1000′ in connection with one or more aspectsof the present invention. In this embodiment, a multi-layer stack 1300is provided, which includes a lower component layer 1310, an uppercomponent layer 1320, and one or more in-between component layer(s)1015. The in-between component layer 1015 may be configured andcharacterized, in one or more implementations, as described above inconnection with FIGS. 10-12B. In this implementation, the secure volume1301 defined within multi-layer stack 1300 extends, by way of example,into upper and lower sensor component layers 1310, 1320, such that (forinstance) active layers of upper and lower sensor component layers 1310,1320 may be included within the secure volume, thereby increasing theamount of integrated circuitry or electronic components provided withinthe stack, notwithstanding a reduced number of component layers in thestack. This can be accomplished, in one embodiment, by moving the lowerand upper tamper-detect circuits 1032, 1033 to, for instance, theouter-most surfaces of the lower and upper component layers 1310, 1320,respectively. As in the example described above, back-end-of-line (BEOL)processing could be employed to define one or more mat-type,tamper-detect circuits to protect the opposite main surfaces of themulti-layer stack 1300. Further, in this configuration,through-substrate vias 1201′ may be provided within the lower and uppersensor component layers 1310, 1320 aligned with respectivethrough-substrate vias 1201 about the periphery or circumference ofin-between component layer 1015 to form the one or more peripheraltamper-detect circuits 1034′ of the tamper-respondent sensor. Monitorcircuitry 1031 of the tamper-respondent electronic circuit structure maybe disposed, for instance, in the active layer of any one or more of thecomponent layers in the multi-layer stack, with monitor circuitry 1031being illustrated in lower sensor component layer 1013, by way ofexample only. Dimensions and operation of the tamper-respondent sensor,and more generally, the tamper-respondent electronic circuit structure,would be similar to those described above. Note in this regard, that theinterconnect lines (or stitch connections) 1210 may be formed near theopposite main surfaces of the multi-layer stack 1300 below, in one ormore implementations, one or more mat-type, tamper-detect circuits (orcircuit layers) of the respective upper and lower tamper-detect circuits1033, 1032.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the invention for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A tamper-respondent assembly comprising: amulti-layer stack comprising multiple discrete component layers stackedand electrically connected together via a plurality of electricalcontacts in between the component layers; a tamper-respondent electroniccircuit structure embedded within the multi-layer stack, thetamper-respondent electronic circuit structure comprising at least onetamper-respondent sensor embedded, at least in part, within at least onecomponent layer of the multiple discrete component layers of themulti-layer stack, the tamper-respondent electronic circuit structuredefining a secure volume within the multi-layer stack; and wherein thetamper-respondent electronic circuit structure is embedded within themulti-layer stack, and the secure volume resides fully within themulti-layer stack.
 2. The tamper-respondent assembly of claim 1, whereinthe multi-layer stack comprises a first component layer, at least onein-between component layer, and a second component layer stackedtogether, the at least one in-between component layer being disposedbetween the first component layer and the second component layer in themulti-layer stack, and wherein the tamper-respondent electronic circuitstructure is associated with the first component layer, the at least onein-between component layer, and the second component layer, with thesecure volume being defined, at least in part, within the at least onein-between component layer.
 3. The tamper-respondent assembly of claim2, wherein the at least one tamper-respondent sensor comprises at leastone lower tamper-detect circuit within the first component layer and atleast one upper tamper-detect circuit within the second component layer.4. A method of fabricating a tamper-respondent assembly comprising:providing a multi-layer stack comprising multiple discrete componentlayers stacked and electrically connected together via a plurality ofelectrical contacts in between the component layers; embedding atamper-respondent electronic circuit structure within the multi-layerstack, the tamper-respondent electronic circuit structure comprising atleast one tamper-respondent sensor embedded, at least in part, within atleast one component layer of the multiple discrete component layers ofthe multi-layer stack, the tamper-respondent electronic circuitstructure defining a secure volume within the multi-layer stack; andwherein the tamper-respondent electronic circuit structure is embeddedwithin the multi-layer stack, and the secure volume resides fully withinthe multi-layer stack.
 5. The method of claim 4, wherein the multi-layerstack comprises a first component layer, at least one in-betweencomponent layer, and a second component layer stacked together, the atleast one in-between component layer being disposed between the firstcomponent layer and the second component layer in the multi-layer stack,and wherein embedding the tamper-respondent electronic circuit structurewithin the multi-layer stack comprises associating the tamper-respondentelectronic circuit structure with the first component layer, the atleast one in-between component layer, and the second component layer,with the secure volume being defined, at least in part, within the atleast one in-between component layer.
 6. The method of claim 5, whereinthe at least one tamper-respondent sensor comprises at least one lowertamper-detect circuit within the first component layer and at least oneupper tamper-detect circuit within the second component layer.
 7. Themethod of claim 6, wherein the at least one tamper-respondent sensorfurther comprises at least one peripheral tamper-detect circuit, the atleast one peripheral tamper-detect circuit defined, at least in part, bya plurality of through-substrate vias extending through the at least onein-between component layer, wherein the at least one upper tamper-detectcircuit, the at least one lower tamper-detect circuit, and the at leastone peripheral tamper-detect circuit electrically connect to monitorcircuity of the tamper-respondent electronic circuit structure andfacilitate defining the secure volume within the multi-layer stack. 8.The method of claim 7, wherein the at least one peripheral tamper-detectcircuit extends between the at least one upper tamper-detect circuit andthe at least one lower tamper-detect circuit, and is disposed about theperiphery of the at least one in-between component layer.
 9. The methodof claim 7, wherein the multi-layer structure resides on a basecomponent layer, the base component layer being a 2.5D interposer. 10.The method of claim 5, wherein the multi-layer stack comprises multiplein-between component layers disposed between the first component layerand the second component layer, the at least one in-between componentlayer being at least one in-between component layer of the multiplein-between component layers, and the at least one tamper-respondentsensor comprises at least one peripheral tamper-detect circuit, the atleast one peripheral tamper-detect circuit including respectivepluralities of through-substrate vias, each plurality extending througha respective component layer of the multiple in-between componentlayers, at least some through-substrate vias of the respectivepluralities of through-substrate vias being electrically interconnectedin the at least one peripheral tamper-detect circuit by respectiveelectrical contacts of the plurality of electrical contacts disposed inbetween component layers of the multi-layer stack.
 11. The method ofclaim 4, further comprising an under-fill material disposed betweenadjacent component layers of the multiple discrete component layers, theunder-fill material surrounding, at least in part, electrical contactsof the plurality of electrical contacts in between the component layers.